The present invention relates to electrodes used in medical treatment and, more particularly, to electrodes employed with radio frequency energy to produce deep heating by hyperthermia.
The therapeutic effects of heat have been known for a long time. Of particular interest, it is has been found that tumors can be heated and, thereby, destroyed by the heat alone or with the heat adding to the effects of other treatment such as chemotherapy. Likewise, it has been known that radio frequency energy can be employed to cause by traditional diathermy apparatus.
Recently, in my U.S. Pat. No. 4,186,729, an electrode was shown which allows radio frequency energy to be employed to cause deep-heating within an animal body. A simplified drawing of an electrode as disclosed therein is shown in FIG. 1. Prior to my Deep-Heating Electrode, a person 10 having a tumor situated deep within his body was virtually unable to have sufficient energy transferred thereto to cause therapuetic heating of the tumor. Before my invention, such heating could only occur effectively by surgically exposing the tumor and placing traditional diathermy electrodes in electrical contact with opposing surfaces of the tissue to cause the energy to pass therethrough. Attempts to use such traditional diathermy apparatus by placing the electrodes in contact with the exterior surfaces of the body merely cause the energy to be dissipated in the skin and subcutaneous fat layers with very little, if any, heating occuring in the deep areas where desired.
According to my invention as disclosed in the above-referenced patent, an electrode 12 in the form of a cylinder, as shown, can be placed about the body of the person 10 over the area of the tumor and deep-heating energy transmitted thereto if the electrode 12 is in the form of a single-turn self-resonant loop which causes a series of concentric force lines of substantially equal energy to be created inside the cylinder.
The construction of such an electrode is typified by the example of FIG. 2 (which appeared as FIG. 2 in the above-referenced patent). In that embodiment, electrode 12 comprises a strip of conductive material formed into a cylinder having the ends thereof in overlapping, non-contacting relationship. While an air dielectric could be employed, it is preferred that a material such as Teflon be disposed between the overlapping ends of electrode 12 such as that labeled 14 in FIG. 2. The area of overlap and the dielectric material are chosen such that when electrode 12 is excited by connecting it a source of radio frequency energy as by providing taps 16 to which a connector 18 providing the RF energy can be connected, maximum energy is transferred.
Typically, the electrodes designed using the above techniques have had an aspect ratio of approximately 2 to 1. That is, the diameter is twice the cylinder length. This has resulted in a very efficient electrode and, in general, heated the desired volume within the cylinder. An additional need, however, has been established for a long cylindrical electrode where the aspect ratio is approximately 0.5 to 1. That is, the diameter being one-half the cylinder length. This added length configuration is desired to heat a greater portion of a limb (i.e., arm, leg) or possibly a larger section of the body, in a uniform manner, thus pre-heating the blood entering the lesion area. It has also been found to have therapeutic benefit for the typical diathermy type treatments such as muscle and joint pain.
In attempting to construct such an electrode of useable dimensions applying the above-described technique of end overlap, considerable problems were encountered. For example, in a cylinder of 13 centimeters diameter and 23 centimeters length, the inductance is very low and, therefore, a large amount of capacity is required to resonate the cylinder. To accomplish resonance with a convenient overlap required a dielectric thickness of 0.007 inches, thus critically limiting the electrode's power handling capability.
Early experiments with such electrodes and variations thereof also indicated a potential problem of non-uniform and un-controlled heat generation distribution throughout the length thereof.
Wherefore, it is the object of the present invention to provide an electrode for use in medical treatment by hyperthermia using the magnetic field approach wherein the electrode has a long length as compared to the diameter and in which the electrode's design can control the distribution of energy over the electrode cylinder length including the production of uniform heating throughout.